The invention relates to a data carrier which can be operated in a contact-bound mode and in a contactless mode and which includes the means specified hereinafter, namely a transmission contact and a further transmission contact which are both mechanically accessible from outside the data carrier, and at least one transmission coil which is inductively accessible from outside the data carrier and which serves to receive a useful HF signal in the contactless mode of the data carrier, and a circuit which has a contact terminal connected to the one transmission contact and which has a further contact terminal connected to the further transmission contact and which includes supply voltage generating means to which a received useful HF signal can be applied and by which a supply voltage for various circuit sections of the circuit of the data carrier can be derived from an applied useful HF signal.
The invention further relates to a circuit for a data carrier which can be operated in a contact-bound mode and in a contactless mode and which includes the means specified hereinafter, namely a contact terminal and a further contact terminal which are both adapted to be connected to transmission contacts which are mechanically accessible from outside the data carrier, and two coil terminals which serve for connection to a transmission coil which is inductively accessible from outside a data carrier and which serves to receive a useful HF signal in the contactless mode of the circuit, and supply voltage generating means to which a received useful HF signal can be applied and by which a supply voltage for various circuit sections of the circuit can be derived from an applied useful HF signal.
Such a data carrier of the type defined in the first paragraph and such a circuit of the type defined in the second paragraph are known, for example from the document WO 96/38814 A1.
With regard to this document reference is made particularly to the known data carrier shown in FIG. 4 of said document and described in the corresponding description. A problem encountered with this known data carrier is that in the contactless mode of the data carrier--when a supply voltage for various circuit sections of the data carrier can be generated with the aid of the supply voltage generating means--a potential difference caused by the generated supply voltage occurs between two transmission contacts which are not required in the contactless mode of the data carrier. This potential difference can reach such a high value that this is impermissible in environments with explosion hazard. Another problem is that in the case that an electrically conductive object, such as for example a coin or a ring on a finger of a user's hand, comes into electrically conductive contact with the two transmission contacts, the resulting short-circuit occurs causes the above-mentioned potential difference to decrease, as a result of which the generated supply voltage is at least affected very strongly and may even totally break down.